1. Field of Invention
The present invention relates to broadband and spectrally-tuned circularly-polarizing reflective film material having symmetrical reflection characteristics on the upper and lower surfaces thereof, and more particularly to a method and apparatus for making the same in an economical manner.
2. Brief Description of Prior Art
In U.S. Pat. No. 5,364,557, applicant has taught how to make CLC film and pigments (i.e. microflakes) therefrom, for use in various applications. The advantage of using such CLC pigments is that color characteristics can be imparted to images painted and printed therewith by virtue of the reflection polarizing properties of CLC film materials. In color printing, and in the fine arts, CLC color inks are known to possess much higher color saturation and brightness than conventional pigment and dyed based inks. This is in contrast with conventional pigments made from inorganic dyes where the color characteristics thereof are imparted to images painted and printed therewith by virtue of the absorption properties of such materials. A direct consequence of the absorption properties of prior art pigments based on inorganic dyes is that they are characterized by low reflection characteristics over their respective spectral bands. This makes the colors less bright than would otherwise be desired in many applications where a premium is provided for highly reflective paints, surface coatings, and the like, e.g. in the automotive industries, in particular.
However, CLC-based pigments based on the teachings of applicant""s U.S. Pat. No. 5,364,557 are not without shortcomings and drawbacks.
For example, applicants have discovered that the reflection characteristics of prior art CLC-based films (and microflakes made therefrom) differ on different sides of the CLC film (and microflakes made therefrom). Consequently, as it is impossible to control microflake surface arrangement during application, the color purity and brightness characteristics of color coatings formed by prior art CLC microflakes are generally non-uniform and inadequate for commercial utility.
Consequently, when using prior art CLC film to manufacture CLC-based pigments as taught in U.S. Pat. No. 5,364,557, it has been impossible to produce color images capturing the colorful aspects of nature in a faithful manner, or color images having color tones and shades demanded by even those endowed with low levels of artistic expression.
Thus there is a great need in the art for improved reflective film material and a method of making the same in a way which avoids the shortcomings and drawbacks of prior art methodologies.
Accordingly, it is a primary object of the present invention to provide reflective film that avoids the shortcomings and drawbacks of prior art reflective films and methods of making the same.
Another object is to provide such reflective film that is circularly polarizing and has improved spectral and band-pass position characteristics for imparting improved color characteristics.
Another object of the present invention is to provide improved light reflective film having a laminated construction, wherein the upper and lower surfaces thereof exhibit symmetrical broadband reflection characteristics over particular regions of the visible band of the electromagnetic spectrum, in order to provide improved light reflectively and brightness when used in the manufacture of colored inks, paints and/or crayons of the present invention
Another object of the present invention to provide CLC film material having symmetrical reflection characteristics, wherein the axis of helical pitch of CLC molecules extends along the thickness dimension of the CLC film (i.e. transverse to the surface thereof), and in which the pitch of the helices of the CLC molecules varies in a non-linear (e.g. exponential) manner along the thickness dimension of the CLC film.
Another object of the present invention is to provide such CLC film having a laminated construction, wherein each surface thereof normal to the helical axis exhibits symmetrical broadband reflection characteristics over the visible band of the electromagnetic spectrum, in order to provide improved light reflectively and brightness when used in the manufacture of super-white polarizing inks, paints and/or crayons of the present invention.
Another object of the present invention is to provide such CLC film, wherein the reflection characteristics over the visible band of the electromagnetic spectrum provide improved light reflectively and brightness when used in the manufacture of super-white polarizing inks and/or paints of the present invention.
Another object is to provide CLC film made from both left-handed and right-handed circularly polarizing material having circularly-polarizing reflection characteristics over the entire visible band of the electromagnetic spectrum, for imparting improved color characteristics.
Another object is to provide a method of fabricating circularly polarizing reflective film with symmetrical reflection characteristics, wherein the film exhibits low optical loss propertiesm and high polarizing efficiency, while lending itself to simplified fabrication and low manufacturing cost.
Another object is to provide a method of fabricating broadband CLC film with symmetrical reflection characteristics, in a way which does not employ ultraviolet dye during the manufacture thereof.
Another object is to provide a method of fabricating broadband circularly polarizing reflective film with symmetrical reflection characteristics, wherein the polymerizable CLC being polymerized is exposed to a non-linear (e.g. exponential) intensity gradient of actinic (e.g. UV) radiation by virtue of light loss within the polymerizable CLC medium, thereby causing a non-linear variation in pitch of helices of the CLC molecules therein.
Another object is to provide a method of fabricating super broadband circularly polarizing reflective film using commercially available constituent CLC polymers and liquid crystal material.
Another object is to provide novel forms of coloring media made from polarizing reflective film having symmetrical reflection characteristics.
These and other objects of the present invention will become apparent hereinafter and in the Claims to Invention.